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Schwenkert S, Fernie AR, Geigenberger P, Leister D, Möhlmann T, Naranjo B, Neuhaus HE. Chloroplasts are key players to cope with light and temperature stress. TRENDS IN PLANT SCIENCE 2022; 27:577-587. [PMID: 35012879 DOI: 10.1016/j.tplants.2021.12.004] [Citation(s) in RCA: 20] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/29/2021] [Revised: 11/16/2021] [Accepted: 12/09/2021] [Indexed: 05/04/2023]
Abstract
Under natural environmental conditions, changes in light intensity and temperature are closely interwoven, and of all organelles, only chloroplasts react strongly upon alterations of these two parameters. We review increasing evidence indicating that changes in chloroplast metabolism are critical for the comprehensive cellular answer in a challenging environment. This cellular answer starts with rapid modifications of thylakoid-located processes, followed by modifications in the stroma and transport activities across the chloroplast envelope. We propose that the 'modulators' involved contribute to plant stress tolerance and that deciphering of their characteristics is essential to understand 'acclimation'. Especially in times of climatic changes, we must gain knowledge on physiological reactions that might become instrumental for directed breeding strategies aiming to develop stress-tolerant crop plants.
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Rottet S, Förster B, Hee WY, Rourke LM, Price GD, Long BM. Engineered Accumulation of Bicarbonate in Plant Chloroplasts: Known Knowns and Known Unknowns. FRONTIERS IN PLANT SCIENCE 2021; 12:727118. [PMID: 34531888 PMCID: PMC8438413 DOI: 10.3389/fpls.2021.727118] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/18/2021] [Accepted: 08/06/2021] [Indexed: 05/10/2023]
Abstract
Heterologous synthesis of a biophysical CO2-concentrating mechanism (CCM) in plant chloroplasts offers significant potential to improve the photosynthetic efficiency of C3 plants and could translate into substantial increases in crop yield. In organisms utilizing a biophysical CCM, this mechanism efficiently surrounds a high turnover rate Rubisco with elevated CO2 concentrations to maximize carboxylation rates. A critical feature of both native biophysical CCMs and one engineered into a C3 plant chloroplast is functional bicarbonate (HCO3 -) transporters and vectorial CO2-to-HCO3 - converters. Engineering strategies aim to locate these transporters and conversion systems to the C3 chloroplast, enabling elevation of HCO3 - concentrations within the chloroplast stroma. Several CCM components have been identified in proteobacteria, cyanobacteria, and microalgae as likely candidates for this approach, yet their successful functional expression in C3 plant chloroplasts remains elusive. Here, we discuss the challenges in expressing and regulating functional HCO3 - transporter, and CO2-to-HCO3 - converter candidates in chloroplast membranes as an essential step in engineering a biophysical CCM within plant chloroplasts. We highlight the broad technical and physiological concerns which must be considered in proposed engineering strategies, and present our current status of both knowledge and knowledge-gaps which will affect successful engineering outcomes.
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Affiliation(s)
- Sarah Rottet
- Realizing Increased Photosynthetic Efficiency (RIPE), The Australian National University, Canberra, ACT, Australia
| | - Britta Förster
- Australian Research Council Centre of Excellence for Translational Photosynthesis, Research School of Biology, The Australian National University, Canberra, ACT, Australia
| | - Wei Yih Hee
- Realizing Increased Photosynthetic Efficiency (RIPE), The Australian National University, Canberra, ACT, Australia
| | - Loraine M. Rourke
- Realizing Increased Photosynthetic Efficiency (RIPE), The Australian National University, Canberra, ACT, Australia
| | - G. Dean Price
- Realizing Increased Photosynthetic Efficiency (RIPE), The Australian National University, Canberra, ACT, Australia
- Australian Research Council Centre of Excellence for Translational Photosynthesis, Research School of Biology, The Australian National University, Canberra, ACT, Australia
| | - Benedict M. Long
- Realizing Increased Photosynthetic Efficiency (RIPE), The Australian National University, Canberra, ACT, Australia
- Australian Research Council Centre of Excellence for Translational Photosynthesis, Research School of Biology, The Australian National University, Canberra, ACT, Australia
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Yuan H, Pawlowski EG, Yang Y, Sun T, Thannhauser TW, Mazourek M, Schnell D, Li L. Arabidopsis ORANGE protein regulates plastid pre-protein import through interacting with Tic proteins. JOURNAL OF EXPERIMENTAL BOTANY 2021; 72:1059-1072. [PMID: 33165598 DOI: 10.1093/jxb/eraa528] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/28/2020] [Accepted: 10/30/2020] [Indexed: 05/19/2023]
Abstract
Chloroplast-targeted proteins are actively imported into chloroplasts via the machinery spanning the double-layered membranes of chloroplasts. While the key translocons at the outer (TOC) and inner (TIC) membranes of chloroplasts are defined, proteins that interact with the core components to facilitate pre-protein import are continuously being discovered. A DnaJ-like chaperone ORANGE (OR) protein is known to regulate carotenoid biosynthesis as well as plastid biogenesis and development. In this study, we found that OR physically interacts with several Tic proteins including Tic20, Tic40, and Tic110 in the classic TIC core complex of the chloroplast import machinery. Knocking out or and its homolog or-like greatly affects the import efficiency of some photosynthetic and non-photosynthetic pre-proteins. Consistent with the direct interactions of OR with Tic proteins, the binding efficiency assay revealed that the effect of OR occurs at translocation at the inner envelope membrane (i.e. at the TIC complex). OR is able to reduce the Tic40 protein turnover rate through its chaperone activity. Moreover, OR was found to interfere with the interaction between Tic40 and Tic110, and reduces the binding of pre-proteins to Tic110 in aiding their release for translocation and processing. Our findings suggest that OR plays a new and regulatory role in stabilizing key translocons and in facilitating the late stage of plastid pre-protein translocation to regulate plastid pre-protein import.
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Affiliation(s)
- Hui Yuan
- Robert W. Holley Center for Agriculture and Health, USDA-ARS, Cornell University, Ithaca, NY, USA
- Plant Breeding and Genetics Section, School of Integrative Plant Science, Cornell University, Ithaca, NY, USA
| | - Emily G Pawlowski
- Department of Plant Biology, Michigan State University, East Lansing, MI, USA
| | - Yong Yang
- Robert W. Holley Center for Agriculture and Health, USDA-ARS, Cornell University, Ithaca, NY, USA
| | - Tianhu Sun
- Robert W. Holley Center for Agriculture and Health, USDA-ARS, Cornell University, Ithaca, NY, USA
- Plant Breeding and Genetics Section, School of Integrative Plant Science, Cornell University, Ithaca, NY, USA
| | - Theodore W Thannhauser
- Robert W. Holley Center for Agriculture and Health, USDA-ARS, Cornell University, Ithaca, NY, USA
| | - Michael Mazourek
- Plant Breeding and Genetics Section, School of Integrative Plant Science, Cornell University, Ithaca, NY, USA
| | - Danny Schnell
- Department of Plant Biology, Michigan State University, East Lansing, MI, USA
| | - Li Li
- Robert W. Holley Center for Agriculture and Health, USDA-ARS, Cornell University, Ithaca, NY, USA
- Plant Breeding and Genetics Section, School of Integrative Plant Science, Cornell University, Ithaca, NY, USA
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Shi Y, He Y, Lv X, Wei Y, Zhang X, Xu X, Li L, Wu JL. Chloroplast SRP54s are Essential for Chloroplast Development in Rice. RICE (NEW YORK, N.Y.) 2020; 13:54. [PMID: 32761436 PMCID: PMC7410889 DOI: 10.1186/s12284-020-00415-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/26/2020] [Accepted: 07/29/2020] [Indexed: 06/11/2023]
Abstract
BACKGROUND The chloroplast signal recognition particle 54 (cpSRP54) is known for targeting the light-harvesting complex proteins to thylakoids and plays a critical role for chloroplast development in Arabidopsis, but little is known in rice. Here, we reported two homologous cpSRP54s that affect chloroplast development and plant survival in rice. RESULTS Two rice cpSRP54 homologues, OscpSRP54a and OscpSRP54b, were identified in present study. The defective OscpSRP54a (LOC_Os11g05552) was responsible for the pale green leaf phenotype of the viable pale green leaf 14 (pgl14) mutant. A single nucleotide substitution from G to A at the position 278, the first intron splicing site, was detected in LOC_Os11g05552 in pgl14. The wild type allele could rescue the mutant phenotype. Knockout lines of OscpSRP54b (LOC_Os11g05556) exhibited similar pale green phenotype to pgl14 with reduced chlorophyll contents and impaired chloroplast development, but showed apparently arrested-growth and died within 3 weeks. Both OscpSRP54a and OscpSRP54b were constitutively expressed mainly in shoots and leaves at the vegetative growth stage. Subcellular location indicated that both OscpSRP54a and OscpSRP54b were chloroplast-localized. Both OscpSRP54a and OscpSRP54b were able to interact with OscpSRP43, respectively. The transcript level of OscpSRP43 was significantly reduced while the transcript level of OscpSRP54b was apparently increased in pgl14. In contrast, the transcript levels of OscpSRP54a, OscpSRP43 and OscpSRP54b were all significantly decreased in OscpSRP54b knockout lines. CONCLUSION Our study demonstrated that both OscpSRP54a and OscpSRP54b were essential for normal chloroplast development by interacting with OscpSRP43 in rice. OscpSRP54a and OscpSRP54b might play distinct roles in transporting different chloroplast proteins into thylakoids through cpSRP-mediated pathway.
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Affiliation(s)
- Yongfeng Shi
- State Key Laboratory of Rice Biology, China National Rice Research Institute, Hangzhou, 310006 China
| | - Yan He
- State Key Laboratory of Rice Biology, China National Rice Research Institute, Hangzhou, 310006 China
| | - Xiangguang Lv
- State Key Laboratory of Rice Biology, China National Rice Research Institute, Hangzhou, 310006 China
- National Key Facility for Crop Gene Resources and Genetic Improvement, Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing, 100081 China
| | - Yanlin Wei
- State Key Laboratory of Rice Biology, China National Rice Research Institute, Hangzhou, 310006 China
| | - Xiaobo Zhang
- State Key Laboratory of Rice Biology, China National Rice Research Institute, Hangzhou, 310006 China
| | - Xia Xu
- State Key Laboratory of Rice Biology, China National Rice Research Institute, Hangzhou, 310006 China
| | - Liangjian Li
- State Key Laboratory of Rice Biology, China National Rice Research Institute, Hangzhou, 310006 China
| | - Jian-li Wu
- State Key Laboratory of Rice Biology, China National Rice Research Institute, Hangzhou, 310006 China
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Tichá T, Samakovli D, Kuchařová A, Vavrdová T, Šamaj J. Multifaceted roles of HEAT SHOCK PROTEIN 90 molecular chaperones in plant development. JOURNAL OF EXPERIMENTAL BOTANY 2020; 71:3966-3985. [PMID: 32293686 DOI: 10.1093/jxb/eraa177] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/27/2020] [Accepted: 04/06/2020] [Indexed: 05/20/2023]
Abstract
HEAT SHOCK PROTEINS 90 (HSP90s) are molecular chaperones that mediate correct folding and stability of many client proteins. These chaperones act as master molecular hubs involved in multiple aspects of cellular and developmental signalling in diverse organisms. Moreover, environmental and genetic perturbations affect both HSP90s and their clients, leading to alterations of molecular networks determining respectively plant phenotypes and genotypes and contributing to a broad phenotypic plasticity. Although HSP90 interaction networks affecting the genetic basis of phenotypic variation and diversity have been thoroughly studied in animals, such studies are just starting to emerge in plants. Here, we summarize current knowledge and discuss HSP90 network functions in plant development and cellular homeostasis.
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Affiliation(s)
- Tereza Tichá
- Department of Cell Biology, Centre of the Region Haná for Biotechnological and Agricultural Research, Faculty of Science, Palacký University Olomouc, Olomouc, Czech Republic
| | - Despina Samakovli
- Department of Cell Biology, Centre of the Region Haná for Biotechnological and Agricultural Research, Faculty of Science, Palacký University Olomouc, Olomouc, Czech Republic
| | - Anna Kuchařová
- Department of Cell Biology, Centre of the Region Haná for Biotechnological and Agricultural Research, Faculty of Science, Palacký University Olomouc, Olomouc, Czech Republic
| | - Tereza Vavrdová
- Department of Cell Biology, Centre of the Region Haná for Biotechnological and Agricultural Research, Faculty of Science, Palacký University Olomouc, Olomouc, Czech Republic
| | - Jozef Šamaj
- Department of Cell Biology, Centre of the Region Haná for Biotechnological and Agricultural Research, Faculty of Science, Palacký University Olomouc, Olomouc, Czech Republic
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6
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Bölter B. En route into chloroplasts: preproteins' way home. PHOTOSYNTHESIS RESEARCH 2018; 138:263-275. [PMID: 29943212 DOI: 10.1007/s11120-018-0542-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/09/2017] [Accepted: 06/20/2018] [Indexed: 06/08/2023]
Abstract
Chloroplasts are the characteristic endosymbiotic organelles of plant cells which during the course of evolution lost most of their genetic information to the nucleus. Thus, they critically depend on the host cell for allocation of nearly their complete protein supply. This includes gene expression, translation, protein targeting, and transport-all of which need to be tightly regulated and perfectly coordinated to accommodate the cells' needs. To this end, multiple signaling pathways have been implemented that interchange information between the different cellular compartments. One of the most complex and energy consuming processes is the translocation of chloroplast-destined proteins into their target organelle. It is a concerted effort from chaperones, receptor proteins, channels, and regulatory elements to ensure correct targeting, efficient transport, and subsequent folding. Although we have discovered and learned a lot about protein import into chloroplasts in the last decades, there are still many open questions and debates about the roles of individual proteins as well as the mechanistic details. In this review, I will summarize and discuss the published data with a focus on the translocation complex in the chloroplast inner envelope membrane.
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Affiliation(s)
- Bettina Bölter
- Department Biologie I, Botanik, Ludwig-Maximilians-Universität, Planegg-Martinsried, Germany.
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Structural components involved in plastid protein import. Essays Biochem 2018; 62:65-75. [DOI: 10.1042/ebc20170093] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2017] [Revised: 01/24/2018] [Accepted: 01/29/2018] [Indexed: 02/04/2023]
Abstract
Import of preproteins into chloroplasts is an essential process, requiring two major multisubunit protein complexes that are embedded in the outer and inner chloroplast envelope membrane. Both the translocon of the outer chloroplast membrane (Toc), as well as the translocon of the inner chloroplast membrane (Tic) have been studied intensively with respect to their individual subunit compositions, functions and regulations. Recent advances in crystallography have increased our understanding of the operation of these proteins in terms of their interactions and regulation by conformational switching. Several subdomains of components of the Toc translocon have been studied at the structural level, among them the polypeptide transport-associated (POTRA) domain of the channel protein Toc75 and the GTPase domain of Toc34. In this review, we summarize and discuss the insight that has been gained from these structural analyses. In addition, we present the crystal structure of the Toc64 tetratrico-peptide repeat (TPR) domain in complex with the C-terminal domains of the heat-shock proteins (Hsp) Hsp90 and Hsp70.
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8
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Bölter B, Soll J. Once upon a Time - Chloroplast Protein Import Research from Infancy to Future Challenges. MOLECULAR PLANT 2016; 9:798-812. [PMID: 27142186 DOI: 10.1016/j.molp.2016.04.014] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/15/2015] [Revised: 04/25/2016] [Accepted: 04/27/2016] [Indexed: 05/08/2023]
Abstract
Protein import into chloroplasts has been a focus of research for several decades. The first publications dealing with this fascinating topic appeared in the 1970s. From the initial realization that many plastid proteins are being encoded for in the nucleus and require transport into their target organelle to the identification of import components in the cytosol, chloroplast envelopes, and stroma, as well as elucidation of some mechanistic details, more fascinating aspects are still being unraveled. With this overview, we present a survey of the beginnings of chloroplast protein import research, the first steps on this winding road, and end with a glimpse into the future.
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Affiliation(s)
- Bettina Bölter
- Department Biologie I-Botanik, Ludwig-Maximilians-Universität, Großhaderner Straße 2-4, 82152 Planegg-Martinsried, Germany; Munich Center for Integrated Protein Science CiPSM, Ludwig-Maximilians-Universität, Feodor-Lynen-Strasse 25, 81377 Munich, Germany.
| | - Jürgen Soll
- Department Biologie I-Botanik, Ludwig-Maximilians-Universität, Großhaderner Straße 2-4, 82152 Planegg-Martinsried, Germany; Munich Center for Integrated Protein Science CiPSM, Ludwig-Maximilians-Universität, Feodor-Lynen-Strasse 25, 81377 Munich, Germany
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Paila YD, Richardson LG, Inoue H, Parks ES, McMahon J, Inoue K, Schnell DJ. Multi-functional roles for the polypeptide transport associated domains of Toc75 in chloroplast protein import. eLife 2016; 5. [PMID: 26999824 PMCID: PMC4811774 DOI: 10.7554/elife.12631] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2015] [Accepted: 03/04/2016] [Indexed: 01/20/2023] Open
Abstract
Toc75 plays a central role in chloroplast biogenesis in plants as the membrane channel of the protein import translocon at the outer envelope of chloroplasts (TOC). Toc75 is a member of the Omp85 family of bacterial and organellar membrane insertases, characterized by N-terminal POTRA (polypeptide-transport associated) domains and C-terminal membrane-integrated β-barrels. We demonstrate that the Toc75 POTRA domains are essential for protein import and contribute to interactions with TOC receptors, thereby coupling preprotein recognition at the chloroplast surface with membrane translocation. The POTRA domains also interact with preproteins and mediate the recruitment of molecular chaperones in the intermembrane space to facilitate membrane transport. Our studies are consistent with the multi-functional roles of POTRA domains observed in other Omp85 family members and demonstrate that the domains of Toc75 have evolved unique properties specific to the acquisition of protein import during endosymbiotic evolution of the TOC system in plastids. DOI:http://dx.doi.org/10.7554/eLife.12631.001 Chloroplasts are a hallmark feature of plant cells and the sites of photosynthesis – the process in which plants harness the energy in sunlight for their own needs. The first chloroplasts arose when a photosynthetic bacterium was engulfed by another host cell, and most of the original bacterial genes have been transferred to the host cell’s nucleus during the evolution of land plants. As a result, modern chloroplasts need to import the thousands of proteins encoded by these genes from the rest of the cell. The chloroplast protein import system relies on a protein transporter in the chloroplast membrane that evolved from a family of bacterial transporters. However, the bacterial transporters were initially involved in protein export, and it was not known how the activity of these transporters adapted to move proteins in the opposite direction. Paila et al. set out to better understand the chloroplast protein import system and produced mutated forms of the transporter in the model plant Arabidopsis thaliana. These experiments revealed that a part of the transporter that is conserved in many other organisms, the “protein transport associated domains”, has been adapted for three key roles in protein import. First, this part of the transporter interacts with the other components of the import system that make the transporter more selective and control which direction the proteins are transported. Second, the domains interact with proteins during transport to help move them across the chloroplast membrane. Finally, the domains recruit other molecules called chaperones, which stop the protein from aggregating or misfolding during the transport process. These activities are similar to those for the bacterial export transporters, but clearly evolved to allow transport in the opposite direction – that is, to import proteins into chloroplasts. The next challenges are to explain how proteins destined for chloroplasts are recognized and transported through the chloroplast’s membrane. DOI:http://dx.doi.org/10.7554/eLife.12631.002
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Affiliation(s)
- Yamuna D Paila
- Department of Plant Biology, Michigan State University, East Lansing, United States
| | - Lynn Gl Richardson
- Department of Plant Biology, Michigan State University, East Lansing, United States
| | - Hitoshi Inoue
- Department of Plant Biology, Michigan State University, East Lansing, United States
| | - Elizabeth S Parks
- Department of Plant Biology, Michigan State University, East Lansing, United States
| | - James McMahon
- Department of Plant Biology, Michigan State University, East Lansing, United States
| | - Kentaro Inoue
- Department of Plant Sciences, University of California, Davis, United States
| | - Danny J Schnell
- Department of Plant Biology, Michigan State University, East Lansing, United States
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Hauser T, Popilka L, Hartl FU, Hayer-Hartl M. Role of auxiliary proteins in Rubisco biogenesis and function. NATURE PLANTS 2015; 1:15065. [PMID: 27250005 DOI: 10.1038/nplants.2015.65] [Citation(s) in RCA: 74] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/15/2015] [Accepted: 04/20/2015] [Indexed: 05/05/2023]
Abstract
Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) catalyses the conversion of atmospheric CO2 into organic compounds during photosynthesis. Despite its pivotal role in plant metabolism, Rubisco is an inefficient enzyme and has therefore been a key target in bioengineering efforts to improve crop yields. Much has been learnt about the complex cellular machinery involved in Rubisco assembly and metabolic repair over recent years. The simple form of Rubisco found in certain bacteria and dinoflagellates comprises two large subunits, and generally requires the chaperonin system for folding. However, the evolution of hexadecameric Rubisco, which comprises eight large and eight small subunits, from its dimeric precursor has rendered Rubisco in most plants, algae, cyanobacteria and proteobacteria dependent on an array of additional factors. These auxiliary factors include several chaperones for assembly as well as ATPases of the AAA+ family for functional maintenance. An integrated view of the pathways underlying Rubisco biogenesis and repair will pave the way for efforts to improve the enzyme with the goal of increasing crop yields.
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Affiliation(s)
- Thomas Hauser
- Department of Cellular Biochemistry, Max Planck Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany
| | - Leonhard Popilka
- Department of Cellular Biochemistry, Max Planck Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany
| | - F Ulrich Hartl
- Department of Cellular Biochemistry, Max Planck Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany
| | - Manajit Hayer-Hartl
- Department of Cellular Biochemistry, Max Planck Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany
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The TIC complex uncovered: The alternative view on the molecular mechanism of protein translocation across the inner envelope membrane of chloroplasts. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2015; 1847:957-67. [PMID: 25689609 DOI: 10.1016/j.bbabio.2015.02.011] [Citation(s) in RCA: 69] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/10/2014] [Revised: 01/19/2015] [Accepted: 02/07/2015] [Indexed: 12/29/2022]
Abstract
Chloroplasts must import thousands of nuclear-encoded preproteins synthesized in the cytosol through two successive protein translocons at the outer and inner envelope membranes, termed TOC and TIC, respectively, to fulfill their complex physiological roles. The molecular identity of the TIC translocon had long remained controversial; two proteins, namely Tic20 and Tic110, had been proposed to be central to protein translocation across the inner envelope membrane. Tic40 also had long been considered to be another central player in this process. However, recently, a novel 1-megadalton complex consisting of Tic20, Tic56, Tic100, and Tic214 was identified at the chloroplast inner membrane of Arabidopsis and was demonstrated to constitute a general TIC translocon which functions in concert with the well-characterized TOC translocon. On the other hand, direct interaction between this novel TIC transport system and Tic110 or Tic40 was hardly observed. Consequently, the molecular model for protein translocation across the inner envelope membrane of chloroplasts might need to be extensively revised. In this review article, I intend to propose such alternative view regarding the TIC transport system in contradistinction to the classical view. I also would emphasize importance of reevaluation of previous works in terms of with what methods these classical Tic proteins such as Tic110 or Tic40 were picked up as TIC constituents at the very beginning as well as what actual evidence there were to support their direct and specific involvement in chloroplast protein import. This article is part of a Special Issue entitled: Chloroplast Biogenesis.
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Bölter B, Soll J, Schwenkert S. Redox meets protein trafficking. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2015; 1847:949-56. [PMID: 25626173 DOI: 10.1016/j.bbabio.2015.01.010] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/25/2014] [Revised: 01/16/2015] [Accepted: 01/19/2015] [Indexed: 11/15/2022]
Abstract
After the engulfment of two prokaryotic organisms, the thus emerged eukaryotic cell needed to establish means of communication and signaling to properly integrate the acquired organelles into its metabolism. Regulatory mechanisms had to evolve to ensure that chloroplasts and mitochondria smoothly function in accordance with all other cellular processes. One essential process is the post-translational import of nuclear encoded organellar proteins, which needs to be adapted according to the requirements of the plant. The demand for protein import is constantly changing depending on varying environmental conditions, as well as external and internal stimuli or different developmental stages. Apart from long-term regulatory mechanisms such as transcriptional/translation control, possibilities for short-term acclimation are mandatory. To this end, protein import is integrated into the cellular redox network, utilizing the recognition of signals from within the organelles and modifying the efficiency of the translocon complexes. Thereby, cellular requirements can be communicated throughout the whole organism. This article is part of a Special Issue entitled: Chloroplast Biogenesis.
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Affiliation(s)
- Bettina Bölter
- Department Biologie I-Botanik, Ludwig-Maximilians-Universität, Großhadernerstr. 2-4, D-82152 Planegg-Martinsried, Germany; Munich Center for Integrated Protein Science CiPSM, Ludwig-Maximilians-Universität, Feodor-Lynen-Strasse 25, D-81377 Munich, Germany
| | - Jürgen Soll
- Department Biologie I-Botanik, Ludwig-Maximilians-Universität, Großhadernerstr. 2-4, D-82152 Planegg-Martinsried, Germany; Munich Center for Integrated Protein Science CiPSM, Ludwig-Maximilians-Universität, Feodor-Lynen-Strasse 25, D-81377 Munich, Germany.
| | - Serena Schwenkert
- Department Biologie I-Botanik, Ludwig-Maximilians-Universität, Großhadernerstr. 2-4, D-82152 Planegg-Martinsried, Germany; Munich Center for Integrated Protein Science CiPSM, Ludwig-Maximilians-Universität, Feodor-Lynen-Strasse 25, D-81377 Munich, Germany
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13
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Murcha MW, Kmiec B, Kubiszewski-Jakubiak S, Teixeira PF, Glaser E, Whelan J. Protein import into plant mitochondria: signals, machinery, processing, and regulation. JOURNAL OF EXPERIMENTAL BOTANY 2014; 65:6301-35. [PMID: 25324401 DOI: 10.1093/jxb/eru399] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The majority of more than 1000 proteins present in mitochondria are imported from nuclear-encoded, cytosolically synthesized precursor proteins. This impressive feat of transport and sorting is achieved by the combined action of targeting signals on mitochondrial proteins and the mitochondrial protein import apparatus. The mitochondrial protein import apparatus is composed of a number of multi-subunit protein complexes that recognize, translocate, and assemble mitochondrial proteins into functional complexes. While the core subunits involved in mitochondrial protein import are well conserved across wide phylogenetic gaps, the accessory subunits of these complexes differ in identity and/or function when plants are compared with Saccharomyces cerevisiae (yeast), the model system for mitochondrial protein import. These differences include distinct protein import receptors in plants, different mechanistic operation of the intermembrane protein import system, the location and activity of peptidases, the function of inner-membrane translocases in linking the outer and inner membrane, and the association/regulation of mitochondrial protein import complexes with components of the respiratory chain. Additionally, plant mitochondria share proteins with plastids, i.e. dual-targeted proteins. Also, the developmental and cell-specific nature of mitochondrial biogenesis is an aspect not observed in single-celled systems that is readily apparent in studies in plants. This means that plants provide a valuable model system to study the various regulatory processes associated with protein import and mitochondrial biogenesis.
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Affiliation(s)
- Monika W Murcha
- Australian Research Council Centre of Excellence in Plant Energy Biology, University of Western Australia, 35 Stirling Highway, Crawley, Western Australia, 6009, Australia
| | - Beata Kmiec
- Department of Biochemistry and Biophysics, Stockholm University, Arrhenius Laboratories for Natural Sciences, SE-10691 Stockholm, Sweden
| | - Szymon Kubiszewski-Jakubiak
- Australian Research Council Centre of Excellence in Plant Energy Biology, University of Western Australia, 35 Stirling Highway, Crawley, Western Australia, 6009, Australia
| | - Pedro F Teixeira
- Department of Biochemistry and Biophysics, Stockholm University, Arrhenius Laboratories for Natural Sciences, SE-10691 Stockholm, Sweden
| | - Elzbieta Glaser
- Department of Biochemistry and Biophysics, Stockholm University, Arrhenius Laboratories for Natural Sciences, SE-10691 Stockholm, Sweden
| | - James Whelan
- Australian Research Council Centre of Excellence in Plant Energy Biology, School of Life Science, La Trobe University, Bundoora, Victoria, 3086, Australia
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14
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Gutierrez-Carbonell E, Takahashi D, Lattanzio G, Rodríguez-Celma J, Kehr J, Soll J, Philippar K, Uemura M, Abadía J, López-Millán AF. The distinct functional roles of the inner and outer chloroplast envelope of Pea (Pisum sativum) as revealed by proteomic approaches. J Proteome Res 2014; 13:2941-53. [PMID: 24792535 DOI: 10.1021/pr500106s] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Protein profiles of inner (IE) and outer (OE) chloroplast envelope membrane preparations from pea were studied using shotgun nLC-MS/MS and two-dimensional electrophoresis, and 589 protein species (NCBI entries) were identified. The relative enrichment of each protein in the IE/OE pair of membranes was used to provide an integrated picture of the chloroplast envelope. From the 546 proteins identified with shotgun, 321 showed a significant differential distribution, with 180 being enriched in IE and 141 in OE. To avoid redundancy and facilitate in silico localization, Arabidopsis homologues were used to obtain a nonredundant list of 409 envelope proteins, with many showing significant OE or IE enrichment. Functional classification reveals that IE is a selective barrier for transport of many metabolites and plays a major role in controlling protein homeostasis, whereas proteins in OE are more heterogeneous and participate in a wide range of processes. Data support that metabolic processes previously described to occur in the envelope such as chlorophyll and tocopherol biosynthesis can be ascribed to the IE, whereas others such as carotenoid or lipid biosynthesis occur in both membranes. Furthermore, results allow empirical assignation to the IE and/or OE of many proteins previously assigned to the bulk chloroplast envelope proteome.
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Affiliation(s)
- Elain Gutierrez-Carbonell
- Plant Nutrition Department, Aula Dei Experimental Station, CSIC , P.O. Box 13034, 50080 Zaragoza, Spain
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15
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Sjögren LLE, Tanabe N, Lymperopoulos P, Khan NZ, Rodermel SR, Aronsson H, Clarke AK. Quantitative analysis of the chloroplast molecular chaperone ClpC/Hsp93 in Arabidopsis reveals new insights into its localization, interaction with the Clp proteolytic core, and functional importance. J Biol Chem 2014; 289:11318-11330. [PMID: 24599948 DOI: 10.1074/jbc.m113.534552] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The molecular chaperone ClpC/Hsp93 is essential for chloroplast function in vascular plants. ClpC has long been held to act both independently and as the regulatory partner for the ATP-dependent Clp protease, and yet this and many other important characteristics remain unclear. In this study, we reveal that of the two near-identical ClpC paralogs (ClpC1 and ClpC2) in Arabidopsis chloroplasts, along with the closely related ClpD, it is ClpC1 that is the most abundant throughout leaf maturation. An unexpectedly large proportion of both chloroplast ClpC proteins (30% of total ClpC content) associates to envelope membranes in addition to their stromal localization. The Clp proteolytic core is also bound to envelope membranes, the amount of which is sufficient to bind to all the similarly localized ClpC. The role of such an envelope membrane Clp protease remains unclear although it appears uninvolved in preprotein processing or Tic subunit protein turnover. Within the stroma, the amount of oligomeric ClpC protein is less than that of the Clp proteolytic core, suggesting most if not all stromal ClpC functions as part of the Clp protease; a proposal supported by the near abolition of Clp degradation activity in the clpC1 knock-out mutant. Overall, ClpC appears to function primarily within the Clp protease, as the principle stromal protease responsible for maintaining homeostasis, and also on the envelope membrane where it possibly confers a novel protein quality control mechanism for chloroplast preprotein import.
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Affiliation(s)
- Lars L E Sjögren
- From the Department of Biological and Environmental Sciences, Gothenburg University, Box 461, 405 30 Gothenburg, Sweden and
| | - Noriaki Tanabe
- From the Department of Biological and Environmental Sciences, Gothenburg University, Box 461, 405 30 Gothenburg, Sweden and
| | - Panagiotis Lymperopoulos
- From the Department of Biological and Environmental Sciences, Gothenburg University, Box 461, 405 30 Gothenburg, Sweden and
| | - Nadir Z Khan
- From the Department of Biological and Environmental Sciences, Gothenburg University, Box 461, 405 30 Gothenburg, Sweden and
| | - Steven R Rodermel
- the Department of Genetics, Development and Cell Biology, Iowa State University, Ames, Iowa 50011
| | - Henrik Aronsson
- From the Department of Biological and Environmental Sciences, Gothenburg University, Box 461, 405 30 Gothenburg, Sweden and
| | - Adrian K Clarke
- From the Department of Biological and Environmental Sciences, Gothenburg University, Box 461, 405 30 Gothenburg, Sweden and.
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16
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Arabidopsis thaliana Tic110, involved in chloroplast protein translocation, contains at least fourteen highly divergent heat-like repeated motifs. Biologia (Bratisl) 2013. [DOI: 10.2478/s11756-013-0310-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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17
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Abstract
SIGNIFICANCE Disulfide-bonded proteins in chloroplasts from green plants exist in the envelope and the thylakoid membrane, and in the stroma and the lumen. The formation of disulfide bonds in proteins is referred to as oxidative folding and is linked to the import and folding of chloroplast proteins as well as the assembly and repair of thylakoid complexes. It is also important in the redox regulation of enzymes and signal transfer. RECENT ADVANCES Green-plant chloroplasts contain enzymes that can form and isomerize disulfide bonds in proteins. In Arabidopsis thaliana, four proteins are identified that are relevant for the catalysis of disulfide bond formation in chloroplast proteins. The proteins' low quantum yield of Photosystem II 1 (LQY1, At1g75690) and snowy cotyledon 2 (SCO2, At3g19220) exhibits protein disulfide isomerase activity and is suggested to function in the assembly and repair of Photosystem II (PSII), and the biogenesis of thylakoids in cotyledons, respectively. The thylakoid-located Lumen thiol oxidoreductase 1 (LTO1, At4g35760) can catalyze the formation of the disulfide bond of the extrinsic PsbO protein of PSII. In addition, the stroma-located protein disulfide isomerase PDIL1-3 (At3g54960) may have a role in oxidative folding. CRITICAL ISSUES Research on oxidative folding in chloroplasts plants is in an early stage and little is known about the mechanisms of disulfide bond formation in chloroplast proteins. FUTURE DIRECTIONS The close link between the import and folding of chloroplast proteins suggests that Hsp93, a component of the inner envelope's import apparatus, may have co-chaperones that can catalyze disulfide bond formation in newly imported proteins.
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18
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Priya S, Sharma SK, Goloubinoff P. Molecular chaperones as enzymes that catalytically unfold misfolded polypeptides. FEBS Lett 2013; 587:1981-7. [PMID: 23684649 DOI: 10.1016/j.febslet.2013.05.014] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2013] [Accepted: 05/06/2013] [Indexed: 10/26/2022]
Abstract
Stress-denatured or de novo synthesized and translocated unfolded polypeptides can spontaneously reach their native state without assistance of other proteins. Yet, the pathway to native folding is complex, stress-sensitive and prone to errors. Toxic misfolded and aggregated conformers may accumulate in cells and lead to degenerative diseases. Members of the canonical conserved families of molecular chaperones, Hsp100s, Hsp70/110/40s, Hsp60/CCTs, the small Hsps and probably also Hsp90s, can recognize and bind with high affinity, abnormally exposed hydrophobic surfaces on misfolded and aggregated polypeptides. Binding to Hsp100, Hsp70, Hsp110, Hsp40, Hsp60, CCTs and Trigger factor may cause partial unfolding of the misfolded polypeptide substrates, and ATP hydrolysis can induce further unfolding and release from the chaperone, leading to spontaneous refolding into native proteins with low-affinity for the chaperones. Hence, specific chaperones act as catalytic polypeptide unfolding isomerases, rerouting cytotoxic misfolded and aggregated polypeptides back onto their physiological native refolding pathway, thus averting the onset of protein conformational diseases.
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Affiliation(s)
- Smriti Priya
- Department of Plant Molecular Biology, Faculty of Biology and Medicine, University of Lausanne, CH-1015 Lausanne, Switzerland
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19
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Sommer M, Rudolf M, Tillmann B, Tripp J, Sommer MS, Schleiff E. Toc33 and Toc64-III cooperate in precursor protein import into the chloroplasts of Arabidopsis thaliana. PLANT, CELL & ENVIRONMENT 2013; 36:970-83. [PMID: 23131143 DOI: 10.1111/pce.12030] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/11/2012] [Accepted: 10/31/2012] [Indexed: 05/08/2023]
Abstract
The import of cytosolically synthesized precursor proteins into chloroplasts by the translocon at the outer envelope membrane of chloroplasts (TOC) is crucial for organelle function. The recognition of precursor proteins at the chloroplast surface precedes translocation and involves the membrane-inserted receptor subunits Toc34 and Toc159. A third receptor, Toc64, was discussed to recognize cytosolic complexes guiding precursor proteins to the membrane surface, but this function remains debated. We analysed Arabidopsis thaliana plants carrying a T-DNA insertion in the gene encoding the Toc64 homolog Toc64-III. We observed a light intensity-dependent growth phenotype, which is distinct from the phenotype of ppi1, the previously described mutant of the TOC34 homolog TOC33. Furthermore, chloroplast import of the model precursor proteins pOE33 and pSSU into chloroplasts is reduced in protoplasts isolated from plants with impaired Toc64-III function. This suggests that Toc64-III modulates the translocation efficiency in vivo. A ppi1 and toc64-III double mutant shows a significant increase in the transcript levels of HSP90 and TOC75-III, the latter coding for the pore-forming TOC component. Remarkably, the protein level of Toc75-III is significantly reduced, suggesting that Toc64-III and Toc33 cooperate in the insertion or stabilization of Toc75-III. Accordingly, the results presented support Toc64 as an import-relevant component of the TOC complex.
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Affiliation(s)
- Manuel Sommer
- Center of Membrane Proteomics, Cluster of Excellence Macromolecular Complexes Frankfurt, Department of Biosciences, Molecular Cell Biology of Plants, Johann-Wolfgang-Goethe University Frankfurt, D-60438 Frankfurt, Germany
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20
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Kikuchi S, Bédard J, Hirano M, Hirabayashi Y, Oishi M, Imai M, Takase M, Ide T, Nakai M. Uncovering the protein translocon at the chloroplast inner envelope membrane. Science 2013; 339:571-4. [PMID: 23372012 DOI: 10.1126/science.1229262] [Citation(s) in RCA: 211] [Impact Index Per Article: 19.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Chloroplasts require protein translocons at the outer and inner envelope membranes, termed TOC and TIC, respectively, to import thousands of cytoplasmically synthesized preproteins. However, the molecular identity of the TIC translocon remains controversial. Tic20 forms a 1-megadalton complex at the inner membrane and directly interacts with translocating preproteins. We purified the 1-megadalton complex from Arabidopsis, comprising Tic20 and three other essential components, one of which is encoded by the enigmatic open reading frame ycf1 in the chloroplast genome. All four components, together with well-known TOC components, were found stoichiometrically associated with different translocating preproteins. When reconstituted into planar lipid bilayers, the purified complex formed a preprotein-sensitive channel. Thus, this complex constitutes a general TIC translocon.
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Affiliation(s)
- Shingo Kikuchi
- Laboratory of Regulation of Biological Reactions, Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka, Japan
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21
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Schwarz C, Bohne AV, Wang F, Cejudo FJ, Nickelsen J. An intermolecular disulfide-based light switch for chloroplast psbD gene expression in Chlamydomonas reinhardtii. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2012; 72:378-89. [PMID: 22725132 DOI: 10.1111/j.1365-313x.2012.05083.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Expression of the chloroplast psbD gene encoding the D2 protein of the photosystem II reaction center is regulated by light. In the green alga Chlamydomonas reinhardtii, D2 synthesis requires a high-molecular-weight complex containing the RNA stabilization factor Nac2 and the translational activator RBP40. Based on size exclusion chromatography analyses, we provide evidence that light control of D2 synthesis depends on dynamic formation of the Nac2/RBP40 complex. Furthermore, 2D redox SDS-PAGE assays suggest an intermolecular disulfide bridge between Nac2 and Cys11 of RBP40 as the putative molecular basis for attachment of RBP40 to the complex in light-grown cells. This covalent link is reduced in the dark, most likely via NADPH-dependent thioredoxin reductase C, supporting the idea of a direct relationship between chloroplast gene expression and chloroplast carbon metabolism during dark adaption of algal cells.
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Affiliation(s)
- Christian Schwarz
- Molekulare Pflanzenwissenschaften, Biozentrum Ludwig Maximilian University Munich, Grosshaderner Strasse, Planegg-Martinsried, Germany
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22
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Teixeira PF, Glaser E. Processing peptidases in mitochondria and chloroplasts. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2012; 1833:360-70. [PMID: 22495024 DOI: 10.1016/j.bbamcr.2012.03.012] [Citation(s) in RCA: 126] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/06/2012] [Revised: 03/21/2012] [Accepted: 03/22/2012] [Indexed: 12/12/2022]
Abstract
Most of the mitochondrial and chloroplastic proteins are nuclear encoded and synthesized in the cytosol as precursor proteins with N-terminal extensions called targeting peptides. Targeting peptides function as organellar import signals, they are recognized by the import receptors and route precursors through the protein translocons across the organellar membranes. After the fulfilled function, targeting peptides are proteolytically cleaved off inside the organelles by different processing peptidases. The processing of mitochondrial precursors is catalyzed in the matrix by the Mitochondrial Processing Peptidase, MPP, the Mitochondrial Intermediate Peptidase, MIP (recently called Octapeptidyl aminopeptidase 1, Oct1) and the Intermediate cleaving peptidase of 55kDa, Icp55. Furthermore, different inner membrane peptidases (Inner Membrane Proteases, IMPs, Atp23, rhomboids and AAA proteases) catalyze additional processing functions, resulting in intra-mitochondrial sorting of proteins, the targeting to the intermembrane space or in the assembly of proteins into inner membrane complexes. Chloroplast targeting peptides are cleaved off in the stroma by the Stromal Processing Peptidase, SPP. If the protein is further translocated to the thylakoid lumen, an additional thylakoid-transfer sequence is removed by the Thylakoidal Processing Peptidase, TPP. Proper function of the D1 protein of Photosystem II reaction center requires its C-terminal processing by Carboxy-terminal processing protease, CtpA. Both in mitochondria and in chloroplasts, the cleaved targeting peptides are finally degraded by the Presequence Protease, PreP. The organellar proteases involved in precursor processing and targeting peptide degradation constitute themselves a quality control system ensuring the correct maturation and localization of proteins as well as assembly of protein complexes, contributing to sustenance of organelle functions. Dysfunctions of several mitochondrial processing proteases have been shown to be associated with human diseases. This article is part of a Special Issue entitled: Protein Import and Quality Control in Mitochondria and Plastids.
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Affiliation(s)
- Pedro Filipe Teixeira
- Department of Biochemistry and Biophysics, Stockholm University, Arrhenius Laboratories for Natural Sciences, SE-106 91 Stockholm, Sweden
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23
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Kriechbaumer V, Abell BM. Chloroplast envelope protein targeting fidelity is independent of cytosolic components in dual organelle assays. FRONTIERS IN PLANT SCIENCE 2012; 3:148. [PMID: 22783268 PMCID: PMC3384937 DOI: 10.3389/fpls.2012.00148] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/04/2012] [Accepted: 06/14/2012] [Indexed: 05/22/2023]
Abstract
The general mechanisms of intracellular protein targeting are well established, and depend on a targeting sequence in the protein, which is recognized by a targeting factor. Once a membrane protein is delivered to the correct organelle its targeting sequence can be recognized by receptors and a translocase, leading to membrane insertion. However, the relative contribution of each step for generating fidelity and efficiency of the overall process has not been systematically addressed. Here, we use tail-anchored (TA) membrane proteins in cell-free competitive targeting assays to chloroplasts to show that targeting can occur efficiently and with high fidelity in the absence of all cytosolic components, suggesting that chloroplast envelope protein targeting is primarily dependent on events at the outer envelope. Efficiency of targeting was increased by the addition of complete cytosol, and by Hsp70 or Hsp90, depending on the protein, but none of these cytosolic components influenced the fidelity of targeting. Our results suggest that the main role of targeting factors in chloroplast localization is to increase targeting efficiency by maintaining recognition competency at the outer envelope.
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Affiliation(s)
| | - Ben M. Abell
- *Correspondence: Ben M. Abell, Biomedical Research Centre, Sheffield Hallam University, Howard Street, Sheffield S1 1WB, UK. e-mail:
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24
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Bölter B, Soll J. Protein Import into Chloroplasts: Dealing with the (Membrane) Integration Problem. Chembiochem 2011; 12:1655-61. [DOI: 10.1002/cbic.201100118] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2011] [Indexed: 11/10/2022]
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